This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. There are number of mammalian proteins that cannot be produced with Se-Methionine bacterial expression systems. For those proteins the phase problem could be solved by adding heavy atoms and use their differential scattering to obtain phase information and generate electron density. The method of halide soaking pioneered by Z. Dauter (NSLS) is one alternative to the Se-Met phasing. Short soaking of the protein crystals with high concentration bromide or iodide solutions results in a surface bound ions. Unfortunately, this modification method suffers from low efficiency. Halide soaking often stresses the protein crystal lattice due to differences in osmotic pressure. Methods for introducing RbBr to the sample covered in oil are being developed. Indications are that this approach offers precise control and pinpoint delivery, minimizing physical and chemical shock to the crystal.